This ppt show concept of Data Link Access, BSD Packet Filter, DLPI, Linux SOCK_PACKET, libpcap–Packet capture Library, libnet: Packet Creation and Injection Library
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Socket Programming- Data Link Access
1. Socket Programming – Data
Link Access
Copyright by Hacking Feder
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2. Data Link Access
If datalink access is provided then, application could watch the packets
received by the datalink layer
Eg. Implementation tcpdump, wireshark, etherial
For that application will put interface in promiscuous mode
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3. Data Link Access
Promiscuous mode allows an application to watch all the packets on the
local interface, not just the packets destined for the host on which the
program is running
It is not useful in switched network to sniff data of computers connected in
LAN (Certain methods available to achieve that)
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4. Data Link Access
Three Common Methods to access Data link layer:
1. BSD Packet Filter (BPF)
2. Data link Provide interface (DLPI)
3. Linux packet SOCK_PACKET interface
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5. BSD Packet Filter
Berkeley Software Distribution (BSD, sometimes called Berkeley Unix) is a
Unix operating system derivative developed and distributed by the
Computer Systems Research Group (CSRG) of the University of California,
Berkeley, from 1977 to 1995
After 1991, BSD was open source
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7. BSD Packet Filter
BPF Filtering is in within kernal
By default print only header value
It will be done before copying the packet
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8. DLPI
It is protocol independent interface designed by AT & T
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9. DLPI
Conceptually similar to BPF
pfmod uses boolean expression for filtering
BPF is 3 to 20 time faster them DLPI
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10. Linux SOCK_PACKET
Create a socket of SOCK_PACKET type
ETH_P_xxx tells the datalink which frame types to pass to the socket for the
frames the datalink receives
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11. Linux SOCK_PACKET
As compare to BPF, and DLPI, here no kernal filtering and buffering
SOCK_PACKET offers filtering by device
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12. libpcap – Packet capture Library
The packet capture library, libpcap, provides implementation-independent
access to the underlying packet capture facility provided by the OS
Currently, it supports only the reading of packets
Support currently exists for BPF under Berkeley-derived kernels, DLPI under
HP-UX and Solaris 2.x, NIT under SunOS 4.1.x, the Linux SOCK_PACKET and
PF_PACKET sockets, and a few other operating systems
This library is used by tcpdump, wireshark and etherial application
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Copyright by Hacking Feder
13. libnet: Packet Creation and Injection Library
libnet provides an interface to craft and inject arbitrary packets into the
network
The library hides many of the details of crafting the IP and UDP or TCP
headers, and provides simple and portable access to writing data link and
raw packets
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Copyright by Hacking Feder